What is the difference between gravity casting and low pressure casting?

May 14, 2020

Delin Machinery is specialized in producing casting equipment such as gravity casting machine and low pressure casting machine. Today we talk about the difference between gravity casting and low pressure casting. No matter what the product is, to judge whether it is good or not, we always use a reference to make a comparison. Only in some cases, A may be more suitable, but in another case, B or C may be more suitable. The same is true for gravity casting and low pressure casting.

so what is the difference between gravity casting and low pressure casting?

As we know, gravity casting refers to the process in which the molten metal is injected into the mold under the influence of the earth’s gravity.
Gravity casting has the following characteristics:
1. There are few pores inside the casting, and the strength of the product after heat treatment can be greatly improved, even exceeding the die-cast product.
2. The product has a low density. Relying on liquid self-weight molding, the density of the product is lower than that of die casting, and its strength is slightly worse, but its elongation is higher.
3. The surface finish of the product is not high. After cooling and shrinking, the cast product is prone to form blast-like pits on the surface. The casting blank produced requires further surface treatment with a polishing machine.
4. Slow filling and low production efficiency.
5. The service life of the mold is longer than that of die casting, and the cost of the mold is low.

Low pressure casting is a casting method in which a liquid alloy is pressed into the mold cavity from below by pressure and solidified under pressure.
The characteristics of low-pressure casting are as follows:
1. The bottom injection type filling is adopted, the metal liquid filling is stable, and there is no splash phenomenon, which can avoid the gas entrapment and the scouring of the mold wall and the core, and improve the casting pass rate.
2. The casting has good formability, which is helpful to form a blank with a clear outline and a smooth surface.
3. The casting has a compact structure and high mechanical properties. When selecting castings with high airtightness requirements, low-pressure casting is used, and the production volume is large.
4. Improve the process yield of raw materials, save the feeder, and improve the metal utilization rate to 90 ~ 98%.
5. The pressure and speed during pouring can be adjusted, so it can be applied to various casting molds (such as metal molds, sand molds, etc.), casting various alloys and castings of various sizes.
6. The casting crystallizes under pressure, the casting has a dense structure, clear outline, smooth surface, and high mechanical properties, which is especially beneficial for the casting of large and thin-walled parts.
7. Because the equipment is mechanized and automated, the labor intensity is low, the labor environment is good, and the production efficiency is greatly improved.

Advantages of low pressure die casting (relative to gravity die casting):
(1) The pouring system of low-pressure casting is very simple, which greatly reduces the amount of alloy melting, on the other hand, it also improves the utilization rate of the metal.
(2) Relative to gravity casting, low-pressure casting is easier to realize mechanically automated production. One worker can operate two or three low-pressure casting machines, and the production efficiency is greatly improved, sometimes it can be increased by more than 3 times, and It means good working conditions and low labor intensity.
(3) However, the relative equipment investment of low-pressure casting is higher than that of gravity casting.
(4) The casting utilization rate is very high. More than 90% have no riser and runner, and the gate is small, so the material cost and processing hours can be greatly reduced.
(5) Obtain perfect castings. Directional solidification is easy to form, and there are few internal defects.
(6) Less involvement of gas and debris. The pressurizing speed can be changed, and the molten metal is filled by laminar flow.
(7) Sand cores can be used.

Taking aluminum alloy casting as an example, the difference between aluminum alloy low-pressure casting and aluminum alloy gravity casting is specifically analyzed:

Type Forming principle Aluminum casting structure Labor intensity Minimum batch Development time Mold cost
Aluminum alloy gravity casting use gravity complex and diverse high 100 short less
Aluminum alloy low pressure casting use air pressure single general 500 long higher

It can be seen from the table comparison that aluminum alloy gravity casting is more suitable for the production of multiple varieties of small batches, short development cycles, and high-quality requirements, while aluminum alloy low pressure casting is suitable for the production of some larger batches, the thickness of aluminum castings is thin, and the structure is suitable for aluminum alloys. Low-pressure casting products, the long development cycle is conducive to the improvement of production technology in the production process.
The typical aluminum alloy low-pressure casting process produces automotive wheels. The structure of this aluminum casting is very suitable for the structural characteristics of the low-pressure casting process, and the production volume is very large. There is enough time to improve production technology. learn more about 
The typical aluminum alloy gravity casting process produces industrial robot castings. The production volume of these aluminum castings is small, the product quality is high, and the development cycle is short. It is necessary to produce high quality without any pores and sand holes in a short time. Aluminum castings.
Through the example of aluminum alloy casting, we can see that reasonable use of the advantages of low-pressure casting and gravity casting can significantly improve production efficiency and company operating benefits.
Finally, Delin machine believes that the purpose and significance of distinguishing between low-pressure casting and gravity casting are that they can make better use of their characteristics, choose a direction that is more conducive to product development, give full play to their respective advantages and characteristics to achieve the ultimate goal of maximizing production.

Delin Machinery is a well-known Chinese foundry machinery manufacturer, which can provide quotation and export of casting machines to various countries. You can click here: casting machine to view more details of our casting machine products. If you want to know more details like are we manufacturers? machine function? support video and more pictures? price list? how to buy? Welcome to Call / WhatsApp or send us Email about any question on the casting machine, please contact us >>>Tel / WhatsApp / WeChat: +86 13960339790, Email: salse16@chinamakeco.com


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